1. Field of the Invention
The present invention relates to an image reading apparatus using a contact image sensor (hereinafter referred to as CIS).
2. Description of the Related Art
Conventional image reading apparatuses using a CIS include the type that uses a white backing roller and the type that uses a white backing plate, both as a backing member opposed to the CIS. An original is passed between the backing member and CIS.
In the type using a white backing roller as a backing member, as shown in FIGS. 7 and 8, originals stacked in an original stacker (not shown), are fed by a paper feeder sheet by sheet, and transported from a paper feeding section 23 through transport rollers 24 and an original guide 25 to a reading device including a CIS 22 and a backing roller 21. The backing roller 21 is rotatable to transport each original by a drive mechanism, not shown, which rotates a backing roller drive shaft 21a. Subsequently, the original leaving the reading device is guided by an original guide 27 and discharged by discharge rollers 26 to an original stacker not shown. In the type using a white backing plate as a backing member, as shown in FIGS. 9 and 10, originals stacked in an original stacker, not shown, are fed by a paper feeder sheet by sheet, and transported from a paper feeding section 23 through transport rollers 24 and an original guide 25 to a reading device including a CIS 22 and a backing plate 31. The original leaving the reading device is guided by an original guide 27 and discharged by discharge rollers 26 to an original stacker not shown.
The CIS 22 included in the reading device has a glass plate 22a defining a reading plane, light-emitting elements 22b such as an LED array, EL or the like, a sensor array 22c for performing a photoelectric conversion of an image formed, and a rod lens array 22d for imaging light reflected by the original on the image sensor array 22c. The CIS 22 is completely sealed to prevent unnecessary sensor outputs due to external light and also to prevent serious defects in image quality such as black streaks caused by entry of dust. The original is passed, face down, between the glass plate 22a defining a reading plane and the backing roller 21 or backing plate 31 placed on the glass plate 22a. As the original is passed over the glass plate 22a of CIS 22, the CIS 22 reads the original in a single scan in a main scanning direction (perpendicular to the direction of movement of the original). The entire original is read before the original completes its movement over the CIS 22. The backing roller 21 and backing plate 31 are formed of a white material or a material of a light color close to white. Areas outside the forward, rearward, left and right edges of the original are read as white. Light reflected by the backing roller is used as a reference luminosity for shading compensation to determine density levels of the light reflected by the original.
However, where, as in the conventional apparatus noted above, a white backing roller is used as the backing member, an increase in reading speed of the image reading apparatus results in a drawback of causing a friction load between the glass plate defining a reading plane of CIS 22 and the backing roller 21, and also in a drawback of increasing manufacturing costs. Where a backing plate is used as the backing member, manufacturing costs may be kept low but a gap is formed between the backing plate 31 and CIS 22 as a result of variations in curvature of CIS 22 and those due to environmental changes. There occurs a further drawback that, since the CIS 22 has a small focal depth, images read could be out of focus and bloomed.
An object of the present invention is to provide an image reading apparatus which may be manufactured at low cost, and yet is effective to suppress blooming.
To fulfill the above object, the invention provides an image reading apparatus comprising a contact image sensor; and a backing plate disposed to be opposite to the contact image sensor, the backing plate being divided in a main scanning direction of the contact image sensor, an original being passed between the contact image sensor and the backing plate so that the apparatus reads an image from the original.
Thus, according to the invention, the backing plate disposed to be opposite to the contact image sensor is divided in the main scanning direction of the contact image sensor. This construction is effective to suppress a gap occurring with variations in curvature of the contact image sensor or variations in processing due to environmental changes.
Further, the invention provides an image reading apparatus comprising a contact image sensor; and a backing plate disposed to be opposite to the contact image sensor, the backing plate being formed of a flexible material, an original being passed between the contact image sensor and the backing plate so that the apparatus reads an image from the original.
Thus, according to the invention, the backing plate disposed to be opposite to the contact image sensor is formed of a flexible material. This construction also is effective to suppress a gap occurring with variations in curvature of the contact image sensor and variations in processing due to environmental changes.
Furthermore, in the invention it is preferable that pressing means is provided for pressing the backing plate against the contact image sensor.
According to the invention, the backing plate is pressed against the contact image sensor by the pressing means, thereby suppressing, with increased effect, the gap occurring with variations in curvature of the contact image sensor and variations in processing due to environmental changes.
In the invention it is preferable that shading compensation means is provided which uses white color of the backing plate as a reference for performing a shading compensation, and the shading compensation means interpolates, into a division of the backing plate, reading data of adjacent white areas among reading data obtained by the contact image sensor.
Thus, according to the invention, the shading compensation means, which uses the white color of the backing plate as a reference for performing a shading compensation, interpolates, into the division of the backing plate, reading data of adjacent white areas among reading data obtained by the contact image sensor. This prevents the division of the backing plate from affecting the shading compensation.
In the invention it is preferable that compensation means is provided to be operable, when reading data of areas other than a division of the backing plate, among reading data obtained by the contact image sensor, represents white color of the backing plate, for interpolating reading data of adjacent white areas or data representing the white color into the division of the backing plate.
Thus, accordingly to the invention, when reading data of areas other than the division of the backing plate, among reading data obtained by the contact image sensor, represent the white color of the backing plate, the compensation means interpolates reading data of adjacent white areas or data representing the white color into the division of the backing plate. This prevents the division of the backing plate from affecting image reading.